1. Field of the Invention
The present invention pertains to certain arrangements of a downhole instrument for sensing well pressures and temperatures, for example, and transmitting signals related thereto by electromagnetic waves to the surface so that wellbore operations can be carried out based on substantially real-time measurements of downhole conditions.
2. Background
Many wellbore operations benefit from real-time or near real-time measurement of downhole conditions, for example, operations such as testing the rate of pressure build-up in the wellbore of an oil or gas production well and pressure and temperature conditions in the wellbore during formation fracturing or treatment operations. Although wellbore instruments have been developed which are connected to a signal conducting cable extending to the surface through the well tubing, such arrangements are not convenient for well operations where fluids are being injected into the well since the cable may interfere with fluid flow and may be damaged by abrasive substances in the fluid or the chemistry of the fluid. Moreover, the expense associated with deploying such instruments is considerable in many well operations.
Other types of instruments have been developed which may be deployed in the well and disconnected from a conveying cable or tubing and then retrieved at a later time. However, these instruments, which have a memory circuit for storing data related to conditions sensed in the well, do not provide real-time information during well operations. The importance of real-time information for certain well operations is described in U.S. patent application Ser. No. 08/169,697, filed Dec. 20, 1993 and entitled: "A Method for Real-Time Process Control of Well Stimulation" by Carl T. Montgomery and Yih-Min Jan and assigned to the assignee of the present invention.
One type of instrument which has been developed for deployment in wellbores provides substantially real-time information or data to the surface and does not require to be connected to a conductive cable extending from the instrument to the surface through the well interior. Such an Instrument includes an electromagnetic wave transmitter adapted to be deployed in a wellbore and capable of transmitting substantially real-time data concerning wellbore conditions to the surface by of a modulated electrical signal transmitted through the earth. U.S. Pat. No. 5,091,725 to Michael F. Gard, and assigned to the assignee of the present invention, describes certain improvements in electromagnetic (EM) wave transmitters adapted for downhole wellbore operations.
Still further, a type of electromagnetic wave transmitter provided by Geoservices, Inc. of Houston, Tex. is also capable of deployment in a wellbore for transmitting electromagnetic wave signals through the earth in a manner which can provide meaningful pressure and temperature information of conditions in a well at selected locations. However, effective deployment of this type of instrument and signal transmitter in wells for certain types of operations has been heretofore undeveloped. It is to this end that the present invention is directed with a view to providing improved arrangements of deploying downhole instruments for selected well operations which improve these operations by providing real-time information at the surface concerning the conditions in the well at the general location of the instrument.